Voltage
Voltage is a difference in electrical potential. Although voltage is sometimes referred to as the electromotive force, voltage is actually a potential difference. Usually voltage is expressed in volts (V), a unit of electrical measurement named after Italian physicist Alessandro Volta.
Voltage refers to the difference in electrical potential between two points, not the electrical potential itself. The difference in electrical potential between two points A and B is defined as the change in potential energy divided by the charge moved. The change in potential energy can be thought of as the negative of the work done to move a charge in an electric field. When a charge q moves in an electric field E from point A to point B, the work done on the charge by the electric field is qEd, where d is the distance between points A and B. In this case, the change in potential energy is equal to -qEd. When thinking about voltage it is useful to use this concept. For instance, if a 12V battery is connected to two parallel plates, the electric field E between the plates has a magnitude equal to the difference in potential of the two terminals divided by the plate separation.
The voltage of a system is often measured by a voltmeter. The voltmeter measures the difference in electrical potential between two points in a circuit. Two main types of voltmeters are the digital and the analog voltmeter. Analog voltmeters are usually based on the d'Arsonval galvanometer and give voltage readings that can vary over a continuous range. Analog voltmeters usually have a continuous scale and a pointer that indicates the voltage. A digital voltmeter yields voltage readings in groups of digits and has no continuous scale. Digital voltmeters are becoming increasingly popular because of ease of use and reduced costs in production.
A potentiometer is another useful device that is used to continuously vary the voltage of a device. It acts as a variable resistor in a circuit. Potentiometers are usually some form of conductive metal tube or wire that has three terminals. The two resistance terminals are attached to the two input voltage conductors of the battery and the other terminal of the potentiometer, movable with respect to the resistance terminals, is attached to the output voltage conductor. The distance between the two resistance terminals and the third terminal can be varied, hence the percentage of the input voltage applied to the circuit. As well as continuously varying the voltage of a device, the potentiometer can be used to measure the electrical potential difference of a device. It is sometimes more useful to use a potentiometer than a voltmeter because the voltmeter itself often draws significant current.
This is the complete article, containing 448 words
(approx. 1 page at 300 words per page).
